Some woven materials are advantageously made by having fill yarns that are not orthogonal to the warp yarns. For instance, material used to make covers for radar antennas, other radar systems, and other types of antennas. These covers may be referred to as “radome covers.” Radome covers may be as large as 80 to 168 feet or larger in diameter and can be mounted on a platform or foundation where they are subject to high wind speeds. In some locations, a cover must be capable of withstanding wind speeds up to 200 mph. Because of their size and the possibly high wind speeds, the covers are often exposed to high stresses in all directions along its surface. The covers must also, in many circumstances, be capable of withstanding the effects of harsh environmental conditions (sun, heavy rain, ice, blowing sand, temperature extremes, high winds, etc.). To accomplish this, the cover may be constructed of multiple layers (plies) having yarns running in different directions. This may be accomplished by taking two plies, each having an orthogonal orientation, and stitching or otherwise bonding the two plies together such that the warp yarns of a first ply are at a 45 degree angle from the warp yarns of a second ply.
These covers are used to protect various antennas. For instance, they are typically used to cover weather radar antennas, air surveillance radar antennas, satellite communication station antennas, and other antenna.
Industrial belts are another woven material based product that may advantageously be made by having fill yarns that are not orthogonal to the warp yarns. These belts are often subject to high stresses due to excess applied tension (required to prevent slippage of the conveyor belt on the machine drive rolls), stretching, heavy loads conveyed by the belt, and high speed movement combined with side to side movement induced by guiding systems or off-tracking problems. Applied tension, thermal extremes and thermal shock, often cause belt distortion (e.g. longitudinal ridges). In addition, tracking problems can occur due to uneven warp yarn tension.
Expansion joints are used to span the distance between rigid ductwork, connecting for example, a metal flue duct with a metal or solid emissions stack in a power plant (the various pipes, ducts, and other conduits herein referred to as “conduits” unless stated otherwise in a claim). The expansion joint compensates for and accommodates dimensional changes associated with the expansion and contraction of the ductwork, as it is exposed to thermal cycling. It acts like a bellows as the solid ductwork expands and contracts as it transitions through heating and cooling cycles. The expansion joint must accommodate stresses, intermittent flexing and environmental conditions (high winds, temperature excursions, sunlight, caustic flue gasses) associated with the application.
Many designs for these applications are limited by current technology in making the individual plies. Individual plies can be oriented such that the angle of the fill yarns with respect to the warp yarns is changed. If not purposefully stabilized, yarns that are non-orthogonal tend to revert to an orthogonal pattern. Thus, if handled, these oriented plies tend to lose their preferred orientation. Further, current methods of holding an oriented ply in place often require that the oriented ply be held by tacking, stitching, or bonding it to some other article. This requirement limits the ability to design custom fabrics which have the best combination of properly constructed plies for a particular application. Further, these techniques are awkward and difficult in terms of manufacturing. It would be preferable to have a system that allows individual plies to be manufactured, where the individual plies are able to maintain their orientation. It would also be preferable to have a multi-ply material where each ply contributes a unique contribution to the overall composition; a material where each ply can have its own geometric configuration of the yarns, its own matrix material, and its own resin content.
Under current processes used to make non-orthogonal fabrics, a process is used wherein the fabric must be handled between the time in which the orientation of the fabric is made non-orthogonal and the time at which the non-orthogonal orientation is set. During this time period, the fabric may tend to revert to an orthogonal orientation. It would be desirable to have a continuous process for setting a non-orthogonal orientation of a fabric that shortens the time period in which the fabric may tend to revert to an orthogonal orientation. If a continuous process will not be used, it would be desirable to be able to better maintain the non-orthogonal orientation in the time period between when the orientation of the fabric is made non-orthogonal and the time when the non-orthogonal orientation is set.
The fabrics of many of these materials are desirably coated. This coating can have the purpose of resisting environmental elements, maintaining physical properties (including strength and interply adhesions), or of otherwise making the woven fabric more functional. When plies that have been fixed together (to hold their orientation) before coating, it is difficult to create a multi-ply material with good wet out during the coating process. Poor wet out leads to internal voids and surface defects (blisters, bubbles, and craters) in the coating—possibly from air trying to escape the voids during the coating process.
The teachings herein below extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.